Black Boxing and Exposure to Light: To ensure uniform hatching of eggs up to 90 to 95
percent, black boxing of silkworm eggs is necessary. During Blue egg stage, the eggs either in
the sheet or loose condition needs to be maintained in the dark which is known as Black
Boxing. Eggs kept on the rearing tray are wrapped with the black cloth or paper to ensure
complete darkness. Temperature, humidity and aeration required for the eggs should be
maintained. It should be kept undisturbed for 48 hours at “pin head” or 24 hours at blue stage.
. On the expected day of hatching, eggs should be exposed to artificial light or bright day light
in the early morning. Sudden exposure of eggs to light stimulates larvae to come out at a time
from the eggshell. Around 90 - 95 % hatching occurs within one to two hours in this process
Brushing of newly hatched silkworms: Brushing is the process of separating the newly
hatched larvae, gently and carefully, from the empty egg shells or egg sheets and transferring
them to the rearing tray. Ideal time for brushing is 8-9 A.M. Mulberry leaves chopped at a size
of 0.5 cm x 0.5 cm are to be sprinkled in a thin layer on the newly hatched larvae. After 15 –
20 minutes, the hatched larvae crawl to the cut leaves. The egg sheets are turned upside down
to transfer the worms along with the leaves on the rearing tray. The worms are then gently
brushed with a feather for transferring the worms to paraffin paper in a rearing tray. The rearing
bed should be provided with wet foam pad around the bed and covered with another paraffin
paper for maintaining proper microenvironment. In case of loose egg double net should be
provided before sprinkling of chopped leaves.
Temperature: Its plays a vital role in the growth of silkworm. Silkworm being a poikilotherm,
its body temperature changes according to the environmental temperature and as such
temperature will have direct effect on the various physiological activities of their systems. With
an increase in temperature the larval growth is accelerated and the larval period is shortened,
while at low temperature, growth is slow and larval period is prolonged. The optimum
temperature for normal growth in chawki larvae is between 26 oC to 28 oC. Temperature above
30 oC directly affects the health of the worms. Temperature lower than 20 oC the growth of
silkworm is retarded specially in chawki stage, with a result the worms becomes week and
susceptible to disease. High temperature also cause drying of leaves in the rearing bed soon
and become unfit for feeding to the tiny silkworm. Increase in temperature decrease silk
conversion. Higher the rearing temp. there is decrease in fecundity. In lower temperatures than
the optimum ones, duration of the larval stage and mortality of larvae are increased.
Humidity: Atmospheric humidity influences the silkworm growth through mulberry leaves in
addition to its direct effect on the silkworm. In case of low humidity the rate of multiplication
of pathogens is slow, but the leaf withers fast, rendering it unfit for the silkworm to eat. As a
result, growth of the larvae slows down causing weakness and irregular moulting. On the other
hand high humidity keeps the quality of leaf better, larvae grow fast but weak in resistance to
pathogens. Hence an optimum humidity (80-90%) during chawki stage has to be maintained
for the healthy growth of the larvae. High relative humidity during mounting lowers the quality
of cocoons.
Harvesting, Assessment and Marketing Of Cocoons, Reasons For Defective Cocoons
And How To Avoid It?
Quality of cocoons varies according to heredity, environmental conditions or combined
action of heredity and environmental factors. All these factors have a close relation with the
value of cocoon filament. Some of the important characters that are known to be influenced by
these factors are:
Cocoon colour: Generally bivoltine cocoons are white and multivoltine cocoons are golden
yellow, greenish yellow, light green, pink or white in colour. These colours except green are
due to the colouring of sericin and will disappear after degumming of raw silk.
Shape and size of cocoons: The shape of cocoon is racial character and can be classified into
many types such as oval, constricted, elliptical, spherical, spindle shaped etc. The number of
cocoons per litre indicates the size of cocoons.
Weight of single cocoon: It is very important from reeling point of view. Cocoon wt. is
dependent on the race. But female cocoons are heavier than the male cocoons. Wt. of cocoons
also variable according to the rearing condition and amount of mulberry leaves fed.
Weight of single cocoon shell: Higher the wt. of cocoon shell more is the raw silk content. Wt.
of cocoon shell is dependent on race, rearing condition and quantity of leaves fed. It also more
in female cocoons
Shell ratio: It is obtained by dividing the wt. of single cocoon shell by the wt. of single cocoon
and multiplied by 100. Shell ratio is higher in male cocoon than the female cocoons and is
dependent on race, environmental conditions, quantity of mulberry leaves fed, the of
mountages used and mounting method adopted.
Length of cocoon filament: Length of cocoon filament has an intimate relation with the
efficiency of reeling operation. Length of cocoon filament differs according to the silkworm
race, rearing and mounting conditions and quality of mulberry leaves fed.
Weight of cocoon filament: It is the wt. of cocoon filament reeled from a single cocoon. It is
directly proportionate to the wt. of cocoon shell but changes according to the reelability of
cocoon. The wt. of cocoon filament is approximately 80-90% of the wt. of the cocoon shell.
Thickness of cocoon filament: The thickness of cocoon filament is expressed in terms of
denier. It is dependent on silkworm race and conditions of rearing and mounting. Cocoons
having small differences in size between filaments of outer and inner layers are superior.
Reelability: This is indicated by easiness of unwinding the cocoon filament and is measured
by the percentage ratio between length of unbroken filament and the length of entire filament.
Reelability differs among different races and humidity during spinning cocoons has a major
role in determining reelability of cocoons.
Raw silk percentage: It is obtained by dividing the wt. of raw silk reeled by the wt. of cocoons
used for reeling and then multiplied by 100. It is dependent on the silkworm race and conditions
of rearing and mounting.
Cleanness: Sometimes knot appears on the filament and ii is a defect in raw silk. This defect
is mostly due to to problems in the cooking and reeling techniques.
Tenacity and Elongation: The tenacity and elongation are important characters of raw silk in
comparison to synthetic fiber. The tenacity of raw silk is represented by the endurable weight
per denier and the elongation is shown in percentage ratio between the length of extended part
of the thread as maximum and the original length. Usually, the tenacity is 3.5 to 4.0 g and
elongation is about 20%.
Reasons for defective cocoons and How to avoid it
During cocooning some cocoons are provided which are non-reelable due to various
reasons. These may be due to genetic disorder, silkworm diseases, improper mounting,
harvesting and transportation etc. These non-reelable cocoons are of different kinds which are
as follows:
Double cocoons: These are the cocoons jointly formed by 2 or more worms. They are large
in size and thick in shell. Such cocoons can not be reeled for raw silk products. However, it
can be used to produce dupion silk. The occurrence of double cocoons depend on kind of
mountages used for spinning, density of spinning larvae, silkworm race also mounting care
Open end pierced cocoons: The reason for this defect is mainly due to the silkworm race
itself or due to piercing of cocoons by maggot of uzi fly.
Soiled cocoons: Cocoons which are soiled by urination or diseased larvae can not be reeled
well. This occurs due to the kind of mountage and high density of mounting. Sometime the
worms die after spinning silk or just after pupation and soil the inner layer of the cocoon shell.
This is due to carelessness in mounting and handling of cocoons.
Thin end cocoons: In this type, one end or both end of a cocoon are very much thin and not
amenable for reeling. It is often due to genetic character, high temperature during incubation,
malnutrition during rearing or strong wind under humid condition in the mounting room.
Deformed cocoons: This cocoon appear when a number of irregular spaces occur in
cocooning framed or when larvae are not healthy.
Thin shell cocoons: Thin shell cocoons occur when the crop is generally bad due to
malnutrition or diseases.
Loose shell cocoons: Cocoon shell is formed loosely due to silkworm race itself and as in
multivoltine also due to high temperature during cocooning.
